Document using mdBook to generate local preview

README.md

@@ -5,3 +5,13 @@ This repo contains documentation around the [Northstar mod](https://github.com/R
 The `docs/` directory contains the content synchronised to the [GitBook Wiki page](https://r2northstar.gitbook.io/).
 
 Use this repo to perform pull requests and open issues to request changes to the wiki content.
+
+## Building locally
+
+Unfortunately, [GitBook](https://www.gitbook.com/) does not offer a way to work and preview edited content locally.
+
+However, under the hood GitBook just uses [Markdown](https://www.markdownguide.org/) files that can be edited using any text editor.
+They can also be previewed to some degree on GitHub directly.
+
+When working locally, [`mdBook`](https://www.markdownguide.org/) can be used to render previews by simply running `mdbook serve`.
+Note that GitBook has a custom extended markdown syntax that is not supported by mdBook but using mdBook results in a rendered version that is good enough to verify the correctness of most changes.